Chapter Four · failure evidence
What Optoelectronic & Photovoltaic Probing got wrong, from 23 dissertations
The records evaluate experimental probing methods, scanning probe characterization, and transport modeling techniques used in optoelectronic and photovoltaic systems. Across these investigations, researchers encountered physical probe degradations, measurement instrumentation limits, and breakdown of theoretical models under non-standard operating conditions. These records come from PhD theses at 11 institutions, 2021 to 2026. Each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Conductive scanning probe microscopy suffers from tip wear, contact barriers, and substrate incompatibilities
Conductive atomic force microscopy and scanning photocurrent microscopy are impaired by non-ideal semiconductor-metal Schottky barriers, slow contact-limited response times, and rapid tip wear or surface oxidation. In addition, thick insulating substrates like diamond prevent conductive probe measurements by obstructing necessary backing plane electrode integration.
Considered and rejected
Considered and rejected: Rejected pure metal coatings or highly doped single-crystal Si tips for conductive AFM due to rapid tip wear, fragility, and surface oxidation.
Scanning Force Microscopy for Materials Analysis · TXST Digital Repository
Considered and rejected
Considered and rejected: Rejected using standard conductive AFM or SPCM due to non-ideal semiconductor-metal Schottky contact barriers and contact-limited millisecond-to-second response times
Imaging photo-carrier dynamics and correlated states in two-dimensional semiconductors · UT Austin
Considered and rejected
Considered and rejected: Backing plane electrodes on diamond for scanning probe microscopy, rejected because the thick insulating diamond substrate prevents conductive AFM (C-AFM) measurements.
Charge and Optical Stability of Color Centers in Diamond for Quantum Applications · ResearchWorks
Scanning and imaging methods degrade under acquisition latency, parasitic capacitance, and weak contrast
Photoconductively gated scanning tunneling microscopy suffers from circuit capacitance and finite switch response times that distort electrical pulses and degrade temporal resolution. Similarly, scanning microwave microscopy lacks sufficient conductivity contrast against reference standards, while high-speed ultrasonic module scanning suffers signal instability and missing pixel artifacts from transducer vibration and acquisition lag.
Tried and failed
photoconductively gated scanning tunneling microscopy applied to ultrafast time-resolved nanoscale measurements. Outcome: too slow. Reason: finite switch response time and circuit capacitance distorted electrical pulses, degrading temporal resolution
Ultrafast nanoscopy and multi-dimensional spectroscopy of processible photovoltaic materials · Imperial
Tried and failed
high-speed contact ultrasonic scanning applied to thin-film solar photovoltaic modules. Outcome: unstable. Reason: Transducer vibration and acquisition lag caused signal instability and missing pixel artifacts at higher scan speeds.
Ultrasonic guided waves for mechanical defects detection on thin-film solar photovoltaic modules · Georgia Tech
Tried and failed
scanning microwave microscopy admittance fitting applied to ultrathin 2D conductive films. Outcome: no signal. Reason: sample conductivity was too close to reference standard, leading to insufficient contrast and poor signal-to-noise ratio
QUANTITATIVE SCANNING MICROWAVE MICROSCOPY OF NANOELECTRONIC MATERIALS AND DEVICES · Cornell
Numerical simulations and equivalent circuit models fail under extreme carrier densities or nanoscale regimes
Equivalent circuit representations of drift-diffusion equations fail to converge when excess carrier densities exceed substrate doping by two orders of magnitude, and standard Randles circuits severely overestimate double-layer discharge rates. Additionally, assuming constant saturation currents in near-field thermophotovoltaic radiative-transport models neglects distance dependence, generating unphysical open-circuit voltages that exceed the semiconductor bandgap.
Tried and failed
constant saturation current in coupled radiative-transport models applied to near-field thermophotovoltaic energy conversion. Reason: neglects distance dependence, producing unphysical open-circuit voltages exceeding the bandgap at nanoscale separations
STUDY OF THE PHOTON CHEMICAL POTENTIAL IN SEMICONDUCTOR RADIATIVE ENERGY CONVERTERS AT MICRO/NANOSCALES · Georgia Tech
Tried and failed
equivalent circuit modeling of drift-diffusion equations applied to semiconductor charge carrier transport simulation. Outcome: did not converge. Reason: excess carrier densities exceeded baseline substrate doping by two orders of magnitude
A novel approach for SPICE modeling of light and radiation effects in ICs · EPFL
Considered and rejected
Considered and rejected: Rejected standard Randles EC with constant Rct because it overestimates double-layer discharge rates by orders of magnitude compared to experiments.
Aspects of dynamics in proton exchange membrane water electrolysis · Leibniz Universität Hannover Repository
Electrical characterization methods yield inaccurate carrier mobility and potential readings
Open-circuit potential measurements fail to track minority carrier quasi-Fermi level splitting during photoanode water oxidation because accumulated holes remain charge-neutral. In mixed ionic-electronic conductors, pulsed voltage space-charge-limited current measurements underestimate carrier mobilities by multiple orders of magnitude compared to established values.
Tried and failed
open circuit potential to track quasi-Fermi levels applied to semiconductor photoanodes during water oxidation. Outcome: no signal. Reason: hole accumulation is charge-neutral, preventing accurate tracking of minority carrier quasi-Fermi level splitting
Charge carrier accumulation and dynamics in metal oxide photoanodes · Imperial
Tried and failed
pulsed voltage space-charge-limited current measurements applied to carrier mobility extraction in mixed ionic-electronic conductors. Outcome: worse than baseline. Reason: extracted carrier mobilities were underestimated by orders of magnitude compared to established values
The properties and consequences of mobile ionic defects in metal halide perovskites · Imperial
Simplified transport models fail to capture conduction physics in organic and disordered semiconductors
Polaron transport theory fails to reproduce band-like charge transport along the high-mobility axes of large-bandwidth organic crystals. Meanwhile, disorder-based transport models are unable to simultaneously fit the charge-density dependence of mobility and the temperature-independent Seebeck coefficient in semiconducting polymers and carbon nanotube networks.
Tried and failed
Polaron transport theory applied to high-mobility large-bandwidth organic crystals. Outcome: did not generalise. Reason: Fails to capture band-like charge transport characteristics in large-bandwidth organic semiconductors along high-mobility axes
Charge transport and device engineering for improvement of thin film transistor · UT Austin
Tried and failed
Disorder-based transport models applied to semiconducting polymers and carbon nanotube networks. Outcome: did not generalise. Reason: Failed to simultaneously fit mobility charge-density dependence and temperature-independent Seebeck coefficient
Left open by the authors
Problems the authors named and did not get to.
Left open
Characterise electrolyte solution ions via ICP-MS to determine the exact redox reaction mechanism and two-phase discharge profile. Blocker: Requires wet-lab access, chemical samples, and an ICP-MS instrument
Ion-selective membranes for hydrogen-metal hybrid redox flow batteries · Imperial
Left open
Optimize VTD deposition parameters and precursor conversion to eliminate hysteresis and increase perovskite solar cell power conversion efficiency. Blocker: Requires physical vapor transport deposition hardware, chemical precursors, and photovoltaic characterization lab equipment.
Left open
Determine whether 2D perovskite capping layers are fundamentally essential or a transitory optimization trend for PSC technology. Blocker: Requires long-term photovoltaic device fabrication, experimental characterization, and physical wet lab testing
Interfacial Engineering: The Key to Boost Perovskite Solar Cells Performance and Stability · EPFL
Left open
Upscale perovskite photovoltaic device fabrication to larger substrates while suppressing J-V hysteresis and improving stability. Blocker: Requires a physical materials synthesis and device fabrication laboratory.
Low Dose Analytical Electron Microscopy of Hybrid Perovskite Photovoltaic Devices · Cambridge
Left open
Optimize transport layers, engineer perovskite interfaces, and apply passivation layers to minimize series resistance and charge recombination. Blocker: Requires a physical materials synthesis and device fabrication laboratory equipped for vapor deposition and perovskite processing.
Fabricating and Tailoring Halide Perovskites for Photovoltaic Applications · MIT
Left open
Investigate the mechanism of the persistent residual charge transfer state recombination in PbS:2,6-F-CA-/PDI beyond 1.8 ns using transient absorption spectroscopy. Blocker: Requires wet lab chemical synthesis and ultrafast transient absorption spectroscopy apparatus.
Designing nanocrystal donor : molecular acceptor interfaces for improved charge and energy transfer · UT Austin
Left open
Resolve S-shaped double diode degradation under thermal aging in polythiophene hole transport layers for perovskite solar cells. Blocker: Requires a wet chemistry and photovoltaic device fabrication/testing laboratory to synthesize and age devices.
Left open
Optimize perovskite solar cell architectures using Me-4PACz hole transport layers, narrower bandgap absorbers below 1.63 eV, and anti-reflective coatings. Blocker: Requires a wet chemistry and vapor deposition laboratory to fabricate and test physical photovoltaic devices.
Left open
Optimize the thickness of the TiO2 layer in monolithic perovskite solar cells to enhance charge transfer. Blocker: Requires a wet lab and fabrication/characterization equipment for solar cells.
INDIGENOUS DEVELOPMENT OF DYE-SENSITIZED SOLAR CELLS AND PERFORMANCE EVALUATION UNDER TEXAS ENVIRONMENT · WTAMU Repository
Left open
Perform wavelength-dependent surface photovoltage measurements on the tetracene/passivation/silicon interface to determine interfacial charge transfer dynamics and polarity. Blocker: Requires fabricated physical photovoltaic bilayer samples and a surface photovoltage spectroscopy laboratory setup.
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